Metal coated cigarette paper

ABSTRACT

A cigarette wrapper having a coating of metal which does not significantly reduce porosity and combustibility of the wrapper but does significantly increase peak burning temperature of the cigarette using the wrapper (the coating weight being preferably about 1 microgram per square millimeter for optimum reduction of biological activity of the smoke from a cigarette using the wrapper). The metals which have been found suitable are the aluminous metals, iron and tin.

United States Patent l 13,ss6,00s

Inventors Alfred Lippmanllr,

Little Rock; Bernard F1ynn Armbrnst, J r., Benton, both 0!, Art. Appl. No. 767,444 Filed Oct. 14, 1968 Patented June 22, 1971 Assignee Reynolds Metals Company Richmond, Va.

Continuation-impart of application Ser. No. 609,384, Jan. 16, 1967, now abandoned.

METAL COATED CIGARETTE PAPER 15 Claims, 2 Drawing Figs.

U.S. CL 131/15 Int. Cl .1 A24d 01/02,

[50]FieldoiSearch.....I1.. 131/1,9, 15.17;]62/139 [56 I References Cited UNITED STATES PATENTS 2.976.190 3/1961 Meyer l3l/15X 3,106,210 10/1963 Reynoldsetal. 131/l5X Primary Examiner-Melvin D. Rein Attorney-Glenn, Palmer, Lyne, Gibbs & Thompson ABSTRACT: A cigarette wrapper having a coating of metal which does not significantly reduce porosity and combustibility of the wrapper but does significantly increase peak burning temperature of the cigarette using the wrapper (the coating weight being preferably about 1 microgram per square millimeter for optimum reduction of biological activity of the smoke from a cigarette using the wrapper). The metals vhich have been found suitable are 'the aluminous metals, iron and tin.

PATENTED JUH22|97I 3588005 PAPER ASH TOBACCO ASH TOBACCO ASH PAPER ASH 8n 5 ALUMINUM SHEATH n ALUMINIZED PAPER CAGARETTE FIG. I (1.2

INVENTORS ALFRED LIPPMAN, JR.

BERNARD FLYNN ARMBRUST, JR. BY

M M %m, -a 2 W m ATTORNEYS METAL COATED CIGARETTE PAPER This application is a continuation-in-part of application Ser. No. 609,384, filed Jan. 16, 1967 now abandoned.

BACKGROUND OF THE INVENTION For some years there has been extensive discussion in medical and public health circles concerning the alleged carcinogenic and other harmful effects of cigarettes. This discussion has been supplemented by the report of the Surgeon General of the United States, confirming that statistical evidence tends to show a higher incidence of throat cancer and lung cancer in the case of smokers, and especially cigarette smokers, than is true of nonsmokers. These carcinogenic effects are usually ascribed to the presence in cigarette smoke of certain polycyclic aromatic hydrocarbon compounds containing fused ring structures. Experimental studies have indicated that carcinogenic compounds are formed during tobacco pyrolysis and are retained in the smoke generated (by the smoking process on cigarettes) because of incomplete combustion during said smoking process.

The combustion of a cigarette during the smoking process is a very complex phenomenon. The volatile components are vaporized by (1) the radiation from the hot zone; (2) the hot gases being given off from the burning zone; and (3) air coming through the hot zone and being heated to cause this vaporization. These vaporized components are subjected to pyrolysis, decomposition, reaction with other components, and condensation in the cooler zones of the cigarette. As the burning zone approaches the areas where previous condensation has occurred, the condensates are again subjected to heat along with fresh tobacco, giving rise to vaporization, decomposition, reaction, etc., all contingent on conditions in the immediate vicinity.

Over 500 chemical compounds have been identified in cigarette smoke. Reduction in carcinogenicity of the smoke from cigarettes could result from burning up more of the tar or of the carcinogens in the smoke, or from imposing conditions whereunder less carcinogens or more anticarcinogens are formed, or by changing the chemical composition of the smoke to give rise to different synergistic effects resulting in a reduction of carcinogenicity.

SUMMARY OF THE INVENTION In accordance with this invention, it has been found that the higher peak burning temperature of cigarettes with more complete, uniform combustion can be achieved by employing, in conjunction with a conventional tobacco filler, a cigarette paper wrapper in which the paper is coated on either or both faces thereof with a thin layer of a metal, such as aluminous metal. The term aluminous metal" as used herein means aluminum and aluminum-base alloys.

The term peak temperature refers to the maximum burning temperature of a cigarette achieved during the smoking process as measured by a thermocouple (platinum platinum plus 13 percent rhodium) with the bead of the thermocouple placed in the center of the transverse cross section and 30 mm. from the end of the cigarette, which is lighted and then smoked through and beyond the thermocouple bead. For smoking to determine tar levels and other characteristics, the cigarette is smoked to a 25 mm. but (including filter, if present). Puffing for smoke analysis and for temperature measurement is carried out with puffs of 35 ml. volume and 2 seconds duration taken at 1-minute intervals on a mechanized smoking machine until the cigarette is burned to the predetermined length.

Close study of the action of the coating indicates that as the metalcoated paper burns, it forms a relatively continuous and unbroken sheath or tube around the burned and burning tobacco. This is in contrast with the same paper and tobacco with the metal coating omitted, in which case the paper wrapper burns to an ash of relatively great porosity, at least partly due to many breaks in the paper ash, thus permitting a higher proportion of air to pass into the cigarette between the burning zone and the adjacent edge of unburned wrapper paper, with resultant decrease in the proportion of air drawn through the burning zone. The relatively less broken and less porous tubular sheath of burned metal-coated paper of the present invention opposes such passing of air into the cigarette radially behind the burning zone: Instead, it acts as a conduit which causes more of the air to flow, during the puff, lengthwise through the end of the cigarette ash, so that more of the air passes through the burning zone across its entire cross section, thereby making more oxygen available for more complete combustion and higher peak burning temperature during each puff. For example, when a conventional cigarette is puffed the temperature rises by about 20 C. (comparing minimum and peak temperatures), while a like cigarette with 1 microgram per square millimeter aluminum coating on the wrapper has a temperature increase of about 140 C. (measured in the middle of the cross section of the cigarette, with unbroken ash at a point 30 mm. from the original lit end of the cigarette). On the other hand, between puffs, the tubular sheath formed by the burned metal-coated wrapper of the invention cuts down on airflow to the burning zone and thus causes the cigarette of the invention to burn between puffs at a temperature which drops to a level lower than that of a corresponding cigarette with uncoated wrapper (e.g., about 20 C. lower). This slows down wasteful burning between puffs, thus offsetting higher rate of combustion during puffs. The peak temperature increase effect, during puffs, seemingly is not a catalytic effect, as aluminum coated or foil strips within the cigarette were tried per US. Pat. No. 2,976,190; but no rise in temperature resulted. In fact, they actually produced a lowering of the temperature.

For purposes of the invention, the optimum thickness of the aluminous metal coating is about 0.8 to about 1.2 micrograms per square millimeter of paper surface. However, a significant increase of peak temperature is obtainable when the average coating thickness is in the broader range of about 0.5 to about 3 micrograms per square millimeter, accounting for an increase in peak temperature of about 50 C. to about C. (compared to the peak temperature of a corresponding cigarette without any amount of said coating).

Thus, the use of metal-coated cigarette paper within the coating weight ranges of the invention, makes it possible, surprisingly and unexpectedly, to raise and to control degree of combustion and peak temperature, with a conventional tobacco filler.

It had been proposed in the prior art, for example, in U.S. Pat. No. 2,976,190,to employ as a cigarette wrapper a strip of cigarette paper completely coated on one side with flocculent aluminum foil, but this involves a coating of a thickness of 0.2 mils or more, which is not only far outside the critical weight range of the present invention, but which, as indicated in the patent, reduces the combustion temperature.

In U.S. Pat. No. 3,106,210, it is proposed to employ as a wrapper for cigarettes, cigarette paper coated on one side with a thin layer of aluminum or aluminum oxide or both, of a thickness between about 3 and 20 millionths of an inch, and preferably 5 to 10 millionths of an inch, for strengthening the ash in order to keep added alumina hydrate or activated alumina granules from falling out, thereby preventing the burning of objects onto which the alumina granules might otherwise fall. The aluminum coating is said to be applied by vacuum deposition in a single flash at less than 1 micron pressure, which suggests that the weight of the coating of aluminum would not be substantially over 0.3 micrograms per square millimeter. Not more than a small temperature rise is dis closed to be possible, due to combustion of the aluminum, contrary in both respects to the results and findings of the present invention.

It has been further found, that the employment of cigarette paper coatings in accordance with the invention, in addition to achieving more complete combustion, maximizing peak temperature and improving ash characteristics, is responsible for a reduction in the biological activity of the tar produced by the combustion of the paper, and of the tobacco. The optimum performance in increasing the degree of combustion is obtained when the aluminous metal coating has an average thickness of about l microgram per square millimeter. The peak temperature increase compared to uncoated wrapper paper drops off as the aluminous metal coating weight decreases, so that about 0.5 micrograms per square millimeter of aluminous metal coating is necessary to achieve the desired minimum peak temperature increase of 50 C. As the aluminous metal coating weight is increased, the peak temperature increase rises in some cases as much as about 120 C. above the peak for the uncoated cigarette, but does not generally continue to improve as the aluminous metal coating weight increases above the optimum of about 1 microgram per square millimeter. However, the aluminous metal coating weight may be increased until such time as the net porosity of the wrapper paper and coating drops to such a low level that the cigarette is hard to keep lighted. As shown in column B in Table l, as much as about 3 micrograms per square millimeter of aluminous metal coating have been successfully used for the purpose of the invention. The paper may be coated on either or both sides so that the total average weight of the aluminous metal present is in the ranges specified above. In the case of other suitable metals, such as iron or tin, the minimum weight is no lower than 0.5 micrograms per square millimeter to increase the peak temperature by 50 C.; e.g., a coating of about 2.5 to 3 micrograms of vacuum-deposited iron has produced a peak temperature increase of about 60 to 70 C., and a coating of about 0.5 to 0.7 micrograms per square millimeter of vacuum-deposited tin has produced a peak temperature rise of about 50 C., compared to like cigarettes with uncoated paper in both cases.

Porosity of the unburned wrapper is defined as the time in seconds for 50 ml. of air to pass through a 1 inch diameter circular area of the paper being tested, under a slight negative pressure (see Greiner test, pages 707l of Apr. 8, 1960 issue of Tobacco Science). The commercially available medium porosity cigarette paper (Ecusta Ref. 556) used in the Table 1 tests has a porosity of about 22.5 seconds, for example. Coating weights of up to 3 micrograms per square millimeter do not reduce the paper porosity substantially enough to have an adverse effect for the purposes of the invention; for example, wrapper papers having aluminum coatings of l and 1.8 micrograms per square millimeter have been found to have porosities of 24.2 and 28.0 seconds, respectively. Cigarette wrappers of greater and lesser porosities are commercially available and can be used without significant effect on the coating weight limits mentioned above. However, more coating weight could be used to offset to some extent the effect of high level of porosity of a particular wrapper paper.

After a cigarette has been burned the same porosity tests cannot be applied to the ash of the wrapper that are applied to the unburned wrapper. in order to obtain a measurement of porosity of the wrapper and cigarette after burning, the following test has been devised: a cigarette is mounted to be smoked at one end of a tube connected to a manometer to read pressure drop through the bumed-out cigarette, to a vacuum source to draw air through the tube from the bumedout cigarette, and to a flowmeter used to establish a standard 17.5 milliliters per second flow of air through the tube from the burned-out cigarette. The cigarette is first smoked until all the tobacco is burned, and the ash is supported so that it will not break or fall away. The pressure drop is small (about 1 mm. or less of water) and hence difficult to measure precisely. However, it has been found that for a given cigarette there is a substantially straight line increase of peak temperature when plotted against increasing pressure drop measured through the bumed-out cigarette. The latter pressure drop rises, but not in a straight line relation, as wrapper paper coating weight is increased. This further demonstrates that the tubular sheath around the tobacco ash of the burning cigarette of the invention is responsible for the desired increase of peak burning temperature.

DESCRlPTlON OF THE PREFERRED EMBODIMENTS The aluminous metal coating on the cigarette paper in the range of about 0.5 to about 3 micrograms per square millimeter does not detrimentally change the porosity of the unburned cigarette paper, but does affect the burning rate and the porosity of the ash formed therefrom. The coating does not burn, nor even ignite, but it appears to melt or sinter without forming appreciable aluminum oxide. It gives a strong ash and provides a substantially unbroken continuous envelope or tube which produces the increased peak temperature phenomenon of the invention. This is believed to be attributable to the fact that the airflow down through the tube provides more oxygen to the burning zone so that there is more complete combustion of the organic matter and a higher peak temperature during puffs. If the ash is knocked off just prior to each puff, it is found that no substantial increase in peak temperature above that of an ordinary cigarette is produced. However, if in smoking a cigarette with the metalcoated paper of the invention the ash is left in place, the peak temperature can be increased by about 50 C., up to about 120 C., and preferably up to about C.

The metal coated cigarette paper may be manufactured by known methods, for example, by vacuum deposition. Regular cigarette paper is coated in this way to provide a metal layer having the desired thickness. This coating may be applied on either or both sides of the paper. However, it is believed to be commercially preferable to coat only the inside surface of the paper so that the outside will have an uncoated appearance (and also, as suggested by another, so that less products of combustion of the paper wrapper will be drawn into the smoke passing through the cigarette).

The deposition of the metal on the cigarette paper may be performed in conventional apparatus adapted for a vacuum metal coating of web materials, and including a vacuum coating chamber, a crucible located inside the chamber for holding molten coating metal, means for maintaining a high vacuum and means for supplying heat to the crucible. The paper is first degassed by a short vacuum treatment and is then passed through the vacuum coating chamber which contains a source 10f aluminum vapor, the chamber being maintained under high vacuum, preferably well below 1 micron Hg absolute. The source of metal vapor is molten metal in a crucible maintained at a temperature well above the melting point of the metal being coated. The effectiveness of the coating may depend on its quality, which in turn is affected by many factors; e.g., degree of vacuum, outgassing of paper, control of paper temperature and presence of contaminants.

The effect of weight of aluminous metal coating of the cigarette paper on peak temperature is shown in the following table:

TABLE 1.-RELATIONSHIP OF ALUMINUM COATING WEIGHT TO PEAK TEMPERATURE Peak temperature 0.)

Column A Column B Weight of coating (micrograms/sq. mm.)

A curve drawn through the peak temperature points indicates that the peak temperature reaches a substantially constant high level best suited for purposes of the invention when the coating weight is in the range of about 0.8 to L2 micrograms per square millimeter. However, for purposes of reaching desirable increases of peak temperature of about 50 C. to about C. above the corresponding peak temperatures of like cigarettes with uncoated wrappers, the average weight of coating is in the range of about 0.5 to 3 micrograms per square millimeter.

The following examples are illustrative but not limiting:

EXAMPLE 1 A cigarette having an outside diameter of 8 millimeters and a length of 80 millimeters was prepared employing conventional cigarette smoking tobacco 1.1 grams) as a filler and a cigarette paper coated with a layer of aluminum having an average thickness of 1.0 micrograms per square millimeter as a wrapper. The peak temperature of the cigarette was 946 C., compared with 842 C. for a similar cigarette employing uncoated paper.

The improvement in the type and degree of combustion is shown in the accompanying drawings, in which FIG. 1 illustrates a cigarette having a wrapper of aluminum coated paper in accordance with the invention, and FIG. 2 illustrates a corresponding conventional cigarette with the metal coating omitted.

In FIG. I, the cigarette 1 which is being smoked, terminates in a burning zone 2, having the approximate configuration shown. The burning zone apex is surrounded by tobacco ash 3 and the burning zone 2 and ash 3 are surrounded by a substantially unbroken and relatively nonporous tubular sheath formed by the combination of aluminum metal, which does not burn, with the ash of the cigarette wrapper paper. During each puff the incoming air preferentially passes lengthwise through the sheath as indicated by the arrows shown in FIG. 1.

In FIG. 2, an ordinary cigarette is being smoked, but in the absence of an aluminous metal coating, the paper wrapper and the tobacco burn, leaving only a porous and brokcn-sur faced ash 11 around the burning zone 12. The shaped combustion zone 12 is considerably shorter than in P16. 1. During each puff, air is drawn as indicated generally by the arrows in FIG. 2, preferentially radially inwardly. Much of the incoming air passes radially inwardly through the periphery of the pyrolysis zone behind and by passing the combustion zone 12. The net effect is that less air is drawn through the burning zone to provide oxygen.

EXAMPLE 2 This example illustrates the effect of coating weight on peak temperature. Samples of commercially available medium porosity cigarette paper (Ecusta Ref. 556) were subjected to vacuum deposition of aluminum to obtain average weights of deposited metal of respectively 0.1, 0.4, 0.8, 1.0 and 1.2 micrograms per square millimeter. cigarettes of 8 millimeters outside diameter and 80 millimeters length were prepared from each sample of coated paper, each containing 1.1 grams of tobacco. These cigarettes were smoked according to standard procedure and average peak temperatures determined. The results are shown under Columan A in Table 1 above.

EXAMPLE 3 In order to compare control cigarettes with cigarettes of the invention, both types were prepared using conventional cigarette smoking tobacco as a filler and a commercially available medium porosity cigarette paper (Ecusta Ref. 556). These cigarettes served as controls. Cigarettes of the invention were prepared using the same batch of cigarette smoking tobacco as above as a filler and the same cigarette paper as above except that it had previously been coated with a layer of aluminum having an average weight of 1.0 micrograms per square millimeter, as a wrapper. Twenty cigarettes of each type were smoked by standard techniques mentioned previously for measuring peak temperature and tar. The cigarettes of both types were 7.5 millimeters in outside diameter and 85 millimeters long, and had a standard tobacco filler content which would amount to about 2.7 pounds per 1,000 cigarettes.

The control cigarettes had an average peak temperature of 820 C. The Cambridge filter method was used to determine both wet and dry particulate matter, to give 29.4 mg. per cigarette wet particulate matter. and 9.1 mg. dry particulate matter, per cigarette. The above-described cigarettes of the invention gave, using the same procedure, 934 C. average peak temperature with 23.1 mg. per cigarette wet particulate matter, and 8.6 mg. per cigarette dry particulate matter.

It will be understood that the principles of the invention may readily be applied to other types of wrapper materials than cigarette paper, such as, for example, tobacco leaves or thin wrapper sheets made of reconstituted tobacco, which are used for little cigars, cigarillos, and the like. Such wrappers may also be coated with metal within the weight ranges previously disclosed.

The following example illustrates the decrease in biological activity obtainable with cigarettes utilizing the aluminous metal coated paper of the present invention:

EXAMPLE 4 Cigarettes were prepared as in Example 3 so that biological activity of the tars produced by smoking said cigarettes could be evaluated by mouse skin painting techniques. The biological activity of the tars was evaluated on a gram for gram basis without regard to the amount of tar produced per cigarette according to the following method:

Representative cigarettes from each batch were tested for weight, air resistance and porosity of the paper, Using these data, cigarettes of a given type were grouped according to weight and pressure drop, and the negative pressure on the smoking machine was adjusted to provide a puff volume of 35 ml. using constant puff pressure of 2 second duration each minute. The smoke was collected in condensers maintained in a dry ice-ethanol bath. The condensed smoke (tar) was removed with acetone and the acetone solution was concentrated to apparent dryness using reduced pressure.

The crude tar obtained in this manner was weighed, dissolved in an equal volume of acetone, and then treated with eight volumes of heptane, added slowly with mixing. The resulting two phases were separated, the upper phase containing nonpolar components was condensed to provide the refined tar" to be used in subsequent bioassays. This heptane soluble fraction possesses all the mouse skin activity present in crude cigarette tar. The batches of refined tar" were prepared in quantities sufficient for a 2-week supply. The production rate was strictly controlled to provide fresh tar at all times. Except during use or chemical manipulation the tar38 was stored at temperatures below 20 C. in low actinic flasks.

lCR/Ha Swiss female mice ingroups of were used for the bioassays beginning at 40-47 days of age. Two days prior to the beginning of the experiment the dorsal hair was clipped using an Oster Progeinic clipper with a size 0000 head and during the course of the experiment the hair was clipped routinely each month. The refined tar from each group of cigarettes was tested at 8% percent concentration with acetone as the solvent. Each animal was treated with 0.25 ml. of test solution applied 10 times a week from Monday through Friday. An additional group of mice was treated only with acetone as negative controls for the experiment. At weekly intervals, each mouse was examined and the number and distribution of any grossly visible tumors was recorded on a weekly data sheet. Animals which died were autopsied with particular attention paid to the skin, lungs, bladder, liver and kidneys. The negative controls, the group treated with refined tar" from regular commercial cigarettes, and the group treated with refined tar from the product of this invention were treated for 75 weeks. Cigarettes utilizing the Example 3 cigarettes of this invention showed a reduction of about 38 percent in the number of mice with cancers over those painted with tar from cigarettes using regular cigarette paper.

None of the tested cigarettes referred to in the above examples contained any hydrous or activated alumina, which should in any event be kept low enough (substantially below 25 percent by weight of the filler) in the cigarettes of the present invention to avoid adverse effects in terms of increased biological activity.

While present preferred embodiments of the invention have been illustrated and described, the invention is not limited thereto but may be otherwise variously embodied within the scope of the following claims.

What we claim is:

ll. A cigarette comprising a tubular wrapper of medium porosity cigarette paper, a tobacco tiller wrapped in said wrapper, and an aluminous metal coating on said wrapper amounting to at least 0.5 micrograms per square millimeter, and not exceeding 3 micrograms per square millimeter, said aluminous metal coating not substantially reducing porosity or combustibility of the wrapper, and said cigarette having a peak temperature characteristic when burned which is at least about 50 C. to about 120 C. higher than that of a cor responding cigarette without said coating.

2. A cigarette according to claim 1 in which the coating amounts to at least about 0.8 micrograms per square millimeter.

3. A cigarette and the like comprising a tobacco filler capa ble of burning to a porous ash, a tubular wrapper of medium porosity combustible sheet material selected from the group consisting of cigarette paper and thin tobacco sheet, said filler being wrapped in said wrapper, and a metal coating on said wrapper amounting to at least 0.5 micrograms per square mil limeter, said coating not exceeding a weight per square millimeter which would substantially increase the difficulty of keeping the cigarette burning or permit substantial thermal conductivity through the coating lengthwise of the cigarette, said metal being selected from the group consisting of an alu minous metal, iron or tin and providing a coating not being combustible during burning of the cigarette and having the capability when the wrapper is burned of forming with the burned wrapper a substantially unbroken and air-impervious tubular sheath of burned metal-coated wrapper material around the burned tobacco ash, said sheath at least partially maintaining said ash during smoking and having the capability of directing air during puffs lengthwise of the cigarette through the burning zone, the cigarette thereby having the characteristic of a peak burning temperature of at least about 50 C. to about 120 C..higher than a corresponding cigarette without said metal coating.

4. A cigarette according to claim 3, in which the metal is iron.

5. A cigarette according to claim 3, in which the metal is tin.

6. A cigarette according to claim 1 in which the wrapper is paper and the coating is aluminum and amounts to about 1 microgram per square millimeter.

7. A cigarette according to claim 1 in which the wrapper is coated only on its inner surface.

8. A cigarette and the like comprising a tubular wrapper of medium porosity combustible sheet material selected from the group consisting of cigarette paper and thin tobacco sheet, a tobacco filler wrapped in said wrapper, and an aluminous metal coating on said wrapper, said coating not significantly reducing porosity and combustibility of the wrapper as compared to a like wrapper without said coating, having sufficiently low thermal conductivity lengthwise of the cigarette to avoid reducing peak temperature of the cigarette when burned, but being present in an amount sufficient to produce a peak temperature of about 50 C. to about C. above the peak temperature of a corresponding cigarette in which said coating is omitted, the amount of said metal coating being about 0.5 to about 3 micrograms per square millimeter.

9. A cigarette according to claim 8 in which said amount of coating being about 0.8 to 12 micrograms per square millimeter.

ill). Cigarette wrapper stock comprising medium porous and combustible material in sheet form selected from the group consisting of cigarette paper and thin tobacco sheet and an aluminous metal coating thereon which has substantially no effect on porosity or combustibility of said material, and which is present in an amount of about 0.5 to 3 micrograms per square millimeter sufficient to produce a peak tempera ture of about 50 C. to about 120 C., when employed as a cigarette wrapper, above the peak temperature of a corresponding cigarette wrapper in which said coating is omitted.

11. Cigarette wrapper stock according to claim ll0 in which the coating amount is about 0.8 to about 1.2 micrograms per square millimeter.

12. Cigarette wrapper stock according to claim 10 in which the sheet material is paper, the coating is aluminum and the amount of the coating is about 1 microgram per square millimeter.

13. A cigarette according to claim 3, in which the metal is aluminum.

M. A cigarette according to claim 3, in which the wrapper is cigarette paper.

[5. A cigarette according to claim 8, in which the wrapper is cigarette paper. 

2. A cigarette according to claim 1 in which the coating amounts to at least about 0.8 micrograms per square millimeter.
 3. A cigarette and the like comprising a tobacco filler capable of burning to a porous ash, a tubular wrapper of medium porosity combustible sheet material selected from the group consisting of cigarette paper and thin tobacco sheet, said filler being wrapped in said wrapper, and a metal coating on said wrapper amounting to at least 0.5 micrograms per square millimeter, said coating not exceeding a weight per square millimeter which would substantially increase the difficulty of keeping the cigarette burning or permit substantial thermal conductivity through the coating lengthwise of the cigarette, said metal being selected from the group consisting of an aluminous metal, iron or tin and providing a coating not being combustible during burning of the cigarette and having the capability when the wrapper is burned of forming with the burned wrapper a substantially unbroken and air-impervious tubular sheath of burned metal-coated wrapper material around the burned tobacco ash, said sheath at least partially maintaining said ash during smoking and having the capability of directing air during puffs lengthwise of the cigarette through the burniNg zone, the cigarette thereby having the characteristic of a peak burning temperature of at least about 50* C. to about 120* C. higher than a corresponding cigarette without said metal coating.
 4. A cigarette according to claim 3, in which the metal is iron.
 5. A cigarette according to claim 3, in which the metal is tin.
 6. A cigarette according to claim 1 in which the wrapper is paper and the coating is aluminum and amounts to about 1 microgram per square millimeter.
 7. A cigarette according to claim 1 in which the wrapper is coated only on its inner surface.
 8. A cigarette and the like comprising a tubular wrapper of medium porosity combustible sheet material selected from the group consisting of cigarette paper and thin tobacco sheet, a tobacco filler wrapped in said wrapper, and an aluminous metal coating on said wrapper, said coating not significantly reducing porosity and combustibility of the wrapper as compared to a like wrapper without said coating, having sufficiently low thermal conductivity lengthwise of the cigarette to avoid reducing peak temperature of the cigarette when burned, but being present in an amount sufficient to produce a peak temperature of about 50* C. to about 120* C. above the peak temperature of a corresponding cigarette in which said coating is omitted, the amount of said metal coating being about 0.5 to about 3 micrograms per square millimeter.
 9. A cigarette according to claim 8 in which said amount of coating being about 0.8 to 1.2 micrograms per square millimeter.
 10. Cigarette wrapper stock comprising medium porous and combustible material in sheet form selected from the group consisting of cigarette paper and thin tobacco sheet and an aluminous metal coating thereon which has substantially no effect on porosity or combustibility of said material, and which is present in an amount of about 0.5 to 3 micrograms per square millimeter sufficient to produce a peak temperature of about 50* C. to about 120* C., when employed as a cigarette wrapper, above the peak temperature of a corresponding cigarette wrapper in which said coating is omitted.
 11. Cigarette wrapper stock according to claim 10 in which the coating amount is about 0.8 to about 1.2 micrograms per square millimeter.
 12. Cigarette wrapper stock according to claim 10 in which the sheet material is paper, the coating is aluminum and the amount of the coating is about 1 microgram per square millimeter.
 13. A cigarette according to claim 3, in which the metal is aluminum.
 14. A cigarette according to claim 3, in which the wrapper is cigarette paper.
 15. A cigarette according to claim 8, in which the wrapper is cigarette paper. 